Build A 6800 System With This Kit by Gary Kay Southwest Technical Products Corp. 219 W. Rhapsody San Antonio TX 78216 If you are one of the many Teletype or low cost video investment up considerably into memory telling the p eop le getting ready to terminal such as the TV since such interfaces typically processor how and what to purchase one of the Typewriter II (February 1975, cost between $75 and $150 do. Without this software reasonably priced Radio Electronics) for data each, and there are more (program), you can pound on microprocessor system kits and program input/output. surprises yet to come. the keyboard all you want on the market today, you This is all well and good So now you've got your and the computer won't do might ask yourself whether or except that in order to attach co mputer, with interface, anything. Computers are no not you will be able to start a terminal, you'll have to attached to your terminal; smarter than their entering programs once you purchase an interface for you're ready to sit down, programming lets them be get it all put together. Of your computer if it is not power up and start typing in and without programming course you can always load supplied with the basic your program, right? Well, they're not very smart at all. programs and data through system. In fact you will not quite. You see, in order How do you get this software the front panel programmer's generally need a separate to be abl e to use the terminal into memory? Well, you console, but most individuals interface for each I/O for either entering programs could load it in from paper or aware of the front panel's (input/output) device or getting data in and out of cassette tape, that is if you s Iow speed and difficult connected to your computer. the computer you must have have a paper tape reader or readability prefer to use a This can run your system a program resident or loaded cassette tape interface (another sizabl,e investment) or you could enter it directly Fig. 1. Block diagram of the SWTPC 6800 system. The address allocations of the elements of the system are from the programmer's noted inside the blocks. console. The problem here is two fold. Software to give the terminal reasonable system control will probably be 6800 around 500 words in length. CPU, • CLOCK & BUFFERS This is far too long to enter - - - from the programmer's console especially when you consider it has to be re-entered every time the system is powered up or after MIKBUG MIKBUG 2K BYTE CONTROL ROM RAM RAM INTERFACE a wayward program EOOO·E1 FF AOOO·A07F 0000·1 FFF 8004·8007 overwrites any of its allocated area of memory. The second problem is that few if any of the manufacturers supply a Iisti ng, paper tape or cassette tape of such a program to begin with. Their terminal control r outi nes are ~------(TT~E~~~::~32) contained within r editor/assembler and higher 72 4 CONTROL INTERFACE MOTHERBOARD Details of the SWTPC 6800 System. This photo illustrates what you see when you remove the cover of a typical SWTPC computer system. This is MCM6810L 1 an assembly of the parts 128X8 RAM POWER which come in the MP-68 SUPPLY kit. MCM6830L "MIKBUG" ROM MC6800 PROCESSOR level language packages which parts and hardware necessary There is a crystal controll ed soft ware pa c k age called not only must be loaded from to build a Motorola 6800 processo r clock driver and "MIKBUG" that the user can some kind of tape reader, but based microprocessor baud rate generator providing 1) enter program or data into require from 4,096 to 8,192 including a 1,024 wOI'd ROM serial interface baud rates of memory from either the words of memory to operate. (read on ly memory) stored 110, 150, 300, 600 and 1200 terminal's keyboard or tape And you thought the operating system with baud for all but the terminal (where applicable), 2) jump interfaces were expensive, 128- word scratch pad control interface which is to and execute a program just check the prices on 8,192 memory, serial interface baud operable at 110 or 300 baud. loaded in memory, 3) list words of memory. Many of rate generator, serial Al so provided is a power programs or data stored in the systems now on the interface, and 2,048 words of up/manual reset circuit which memory, on the terminal or market are supplied with an memory for $450. This res tarts the ROM stored tape (where applicab le) , ' 4) amount of memory with the article gives a description of mini-operating system examine and/or change the basic unit which is the microprocessor and whenever activated. Full I/O contents of the internal CPU considerably less than what mother board. A future buffering is provided for the registers,S) exam ine and/or might actually be needed for article will describe the power 16 address lines and eight change the contents of useful programming. supply, memory and interface bidirectional data lines with specified memory locations. So what's the alternative? boards. these and other connections These operations are Well, the system presented in made to the rest of the performed using a· 20 mA this article has been designed The Microprocessor/System system through the mother current loop Teletype or an toe lim ina te the afore­ Board (MP-A) board via a 50-pin connector. RS-232C compatible serial mentioned problems and Th e M icroprocessor/ Power for the board is ASCII terminal. allow th e user to have a System Board (coded MP-A) derived from a +5 volt This ROM mini-operating powerful and fully functional is the primary logic board for regulator fed from the system does not have to be system at a minimum cost the system. It is a 51/2" x 9" system's unregulated 7 volt, loaded from tape and it (see Fig. 1). The entire double sided plated-through 10 Amp power supply. cannot be overwritten. It is system is built around the hole circuit board containing Average current consumption a I ways there at your Motorola MC6800 the 6800 microprocessor for the board is 0.8 Amps. fingertips - just pressing the microprocessor and its family chip, the 6830 ROM which The mini-operating system RESET button or simply of support devices. The stores the mini-operating stored in the 6830 ROM on powering the system up computer itself is being made system and the 6810, this board has got to be one a utomatically restarts this avai lab le in kit form including 128-word scratch pad random of the most outstanding firm ware (RO M stored the chassis, cover, power access me mory (RAM) features of this system. It is software). When activated, supply and all circuit boards, needed by the ROM . through this Motorola written this system responds with a 73 to store the program co unter FFFF carriage retu rn, line feed and input/output. In fact, since 1 and/or processor data during r"~ then prints a * on the the character input/output terminal at which time you subroutin es are already stored branch to subroutine (BSR), may enter various single within the operating system jump to subroutine USR), MINIBUGI character control commands ROM, they can be used by push (PHS) or interrupt TEST PATTERN (NOT USED) such as M for memory your programs simply by routines. The index register is f-------- examine/change, L for load loading or storing the a 16-bit register generally EIFF from tape, P for punch or list, characters to be handl ed in used as an address pointer for MIKBUG ROM R for exam ine regi sters or G the pro per register and many processor instructions. EOOO for go to and execute a ex e cut in g a j u m p to There are 72 basic loaded program . A program subroutine (jSR). instructions for the 6800 :::':::: debug routine can also be The Motorola MC6800 microprocessor system (Fig. implemented by using the microprocessor chip is the 3) with most of the 72 A07F software interrupt (SWI) element around which this utilizing several of the seven MIKBUG instruction as a " breakpoint" entire system is built. It is an possible addressing modes: RAM which forces a jump from 8-bit parallel processor with A c cum u I a to r, imp li e d, AOOO you r program to the eight bidirectional data lin es relative, direct, imm ediate, operating system to allow and 16 address lines giving it extended and indexed. ~ ~r-- you to exam ine the contents an addressing capability of up • Accumulator In of memory and/or the CPU to 65,536 words. There is no accumulator addressing, 1/0 PORT 80lF registers. All data entered or distinction between memory either accumulator A or NO.7 80lC 1/0 PORT 80lB displayed through the and I/O addressing on this accumulator B must be system, therefore, all specified. NO.6 8018 terminal is in convenient 1/0 PORT 8017 hexadecimal (b ase 16) input/output data transfers • Implied In implied NO.5 8014 notation. Th is means you can are hand led just as are the addressing the instruction 1/0 PORT 8013 type in a command to load memory transfers. Th is means code itself specifies the NO.4 8010 1/0 PORT 800F address location A00016 with the I/O interfaces must have operand (stack pointer, NO .3 800C 9E16 instead of setting 24 their own allocated memory index register, etc.) .